package q303;

/**
 * Created by brss on 2018/9/17.
 */
public class SegmentTree<E> {

    private E[] tree;
    private E[] data;
    private Merger<E> merger;

    public SegmentTree(E[] arr, Merger<E> merger) {

        this.merger = merger;

        data = (E[])new Object[arr.length];
        for (int i = 0 ; i < arr.length ; i++) {
            data[i] = arr[i];
        }
        tree = (E[])new Object[4 * arr.length];
        buildSegmentTree(0, 0,data.length - 1);
    }

    // 在treeIndex 的位置创建表示区间[l...r]的线段树
    private void buildSegmentTree(int treeIndex, int l, int r) {

        if ( l == r){
            tree[treeIndex] = data[l];
            return;
        }

        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);

        int mid = l + (r - l) / 2;
        buildSegmentTree(leftTreeIndex, l, mid);
        buildSegmentTree(rightTreeIndex, mid + 1, r);
        tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
    }

    public E get(int index) {
        if (index < 0 || index >= data.length)
            throw new IllegalArgumentException("Index is illegal");
        return data[index];
    }

    // 返回完全二叉树的数组表示中，一个索引所表示的元素的左孩子节点的索引
    private int leftChild(int index) {
        return 2*index + 1;
    }

    //返回完全二叉树的数组表示中，一个索引所表示的元素的右孩子节点的索引
    private int rightChild(int index) {
        return 2*index + 2;
    }

    //返回区间[queryL, queryR]的值
    public E query(int queryL, int queryR) {
        if (queryL < 0 || queryR >= data.length || queryL>queryR)
            throw new IllegalArgumentException("Index is illegal");
        return query(0, 0, data.length - 1, queryL, queryR);
    }

    //在以treeID为根的线段树中[l...r]的范围中，搜索区间[queryL,queryR]的值
    private E query(int treeIndex, int l, int r, int queryL, int queryR) {
        if (l == queryL && r == queryR) {
            return tree[treeIndex];
        }

        int mid = l + (r-l)/2;
        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);
        if (queryL >= mid + 1)
            return query(rightTreeIndex, mid + 1, r, queryL, queryR);
        else if (queryR <= mid)
            return query(leftTreeIndex, l, mid, queryL, queryR);

        //要搜索的区间，即不完全再左边，也不完全在右边
        E leftResult = query(leftTreeIndex, l, mid, queryL, mid);
        E rightResult = query(rightTreeIndex, mid + 1, r, mid + 1, queryR);
        return merger.merge(leftResult, rightResult);
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();

        res.append("[");
        for (int i = 0 ; i < tree.length ; i++) {
            if (tree[i] != null)
                res.append(tree[i]);
            else
                res.append("null");
            if (i != tree.length - 1)
                res.append(", ");
        }
        res.append("]");
        return res.toString();
    }
}
